From your original post, I couldn't tell that you had given it that much thought. The accounts of Jesus' early life are different but they can be reconciled and are not mutually exclusive - https://www.ncregister.com/blog/jimmy-akin/how-the-accounts-of-jesus-childhood-fit-together-6-things-to-know-and-share

According to the Cosmological Argument from Contingency, the universe itself is tangible proof. If you're willing, please take a look at this - Five Arguments for God

Is it just one book or is it a set of books written by multiple authors with different perspectives that corroborate each other? Is it just your relatives making this claim or has the claim been made by millions of people for thousands of years? Do other writings exist besides the book you mentioned that support the existence of this "fellow"? If the answer to these questions is "Yes" then maybe it shouldn't be dismissed so casually.

Not that it's any more or less credible, but that's a Fox network website and not the Fox News website.